More than a dozen countries, including the United States, will submit a formal request tomorrow for a Security Council debate on the Soviet invasion of Afghanistan.

This decision was made today at a strategy session in the British mission here attended by representatives from all geographical regions. The letter of request is intentionally noncommittal, asking for an urgent meeting of the council "to consider the situation in Afghanistan and its implications for international peace and security."

Western and Asia diplomats expressed a hope that the council might meet publicly on the question as early as Friday evening. The letter will be submitted tomorrow afternoon to French Ambassador Jacques Leprette, the council president for January.

The initiative in requesting the meeting was taken by a group of Islamic countries led by Pakistan. The United States, Britain and other Western nations have committed themselves to joining the request for U.N. action, and there is hope among them that as many as 40 governments eventually will be added.

"The plan is to get as broad a base as possible," said one of the Asian diplomats spearheading the drive for a council debate. "Physically, on the ground, we do not realistically expect that this will change Moscow's mind about its action in Afghanistan. But it will legitimize the by the guerrillas fighting there.

"It will mean that the Russians will be acting in the glare of international awareness, and it will help the guerrillas fighting there to get guns and aid."

Pakistan is taking the lead in generating a council debate because it fears that Soviet troops now in Afghanistan soon will strike across the border against refugee camps that Moscow sees as guerrilla bases.

A spokesman for the U.N. High Commissioner for Refugees said that as of today there are 387,575 Afghans in the camps supervised by the U.N. agency in Pakistan.

U.S. officials indicated that the council debate on Afghanistan is likely to proceed through the weekend. This may bring it into a time conflict with another volatile world crisis -- the Iranian situation, which is scheduled for further council consideration Monday.

Earlier this week, the council approved a U.S. resolution calling for U.N. Secretary General Kurt Waldheim to travel to Tehran to try to secure the release of American hostages held in the U.S. Embassy there.

If Waldheim's mission does not succeed by Jan. 7, the resolution imposes sanctions that are to be discussed at the Monday meeting. Waldheim arrived in Tehran yesterday, and reports of his meetings so far with Iranian officials have provided little encouragement.

The Security Council currently has only 14 members -- one short of its legal complement under the U.N. charter -- because the General Assembly remains stymied by a three-month long contest between Cuba and Colombia over the 15th seat.

But Western diplomats feel confident that a ruling Monday by U.N. legal counsel Eric Suy, stating that the council can function legitimately with only 14 members, will not be contested.

Although Cuba has indicated disagreement with the ruling, the Soviet Union has privately decided not to challenge the legality of council actions under present circumstances.